Vacuum coating



May 12, 1959 J. SCHWINDT VACUUM COATING Filed Feb. e, 1956 IN VEN TOR. JOHANNES SCHW/NDT kwn Q E Q ATTORNEYS United States Patent VACUUM COATING Johannes 'Schwindt, Langendiebach, Kreis, Hanan, Germany, assignor to W. C. Heraeus, G.m.b.H., Hanan, Germany, a German company Application February 6, 1956, Serial No. 563,742

3 Claims. (Cl. 118-49) This invention relates to apparatus for coating articles with thin layers of a material vaporized in a vacuum.

The apparatus of this invention is adapted for vacuum coating of articles with a material which is vaporized by any one of the several well known methods, such as, ordinary evaporation, cathode sputtering, or the thermal decomposition of the gaseous compounds by use of glow discharge plates to produce a desirable coating material. The material to be evaporatedand deposited on the article by the apparatus of this invention may be any of the usual. and well known metallic, dielectric, organic or inorganic materials.

In conventional apparatus for vacuum coating, the coating. material not only deposits on the article to be coated, but also finds its way into undesired parts of the vacuum apparatus. For example, the coating material sometimes is carried into the vacuum pumping system and impairs the efficiency of the pumps, notably diffusion pumps which are particularly sensitive to impurities. Attempts have been made prior to thiseinvention to prevent the unwanted diffusing of the coating material by installing plates between the source of coating material vapor and the elements in the apparatus to be protected from unwanted coating. The prior elements used to prevent the unwanted spread of the coating material have been cumbersome and awkward, particularly in systems in which the articles to be coated are supported on a rotatable r'ack. bb l, Unwanted diffusing of the coating materialha's' been especially troublesome in apparatus adapted for the production of selenium-coated, light-sensitive semi-conductors due to the tendency of the selenium to diffuse extensively. For example, in past operations, articles have been coated with selenium by fastening the articles to the outside of a rotatable drum located above a source of selenium vapor. The disadvantage of this prior ap-. paratus is that a great amount of selenium deposits on the walls of the apparatus and finds its way into the connections for the vacuum pumps. Selenium is very injurious to the latter, and impairs the efiiciency of the coating apparatus. In addition to the lost time for repairs of the prior apparatus, a large amount of selenium is lost and wasted, resulting in increased costs of operation.

The present invention provides coating apparatus in which the coating material is prevented from spreading .to unwanted parts of the coating apparatus and particularly is excluded from the sensitive parts of the vacuum system.

Briefly, the vacuum coating apparatus of this invention includes a vacuum-tight outer vessel adapted to be evacuated. Means are provided for evaporating a coating material, and a substantially enclosed processing chamber is disposed within the outer vessel and adapted to contain the articles to be coated, the coating material, and the means for evaporating the coating material.

Preferably the processing chamber is drum-like in its cross-section, and is adapted to be rotated coaxially "ice within the outer vessel and about the evaporating source of coating material. The interior of the processing chamber is adapted to hold the articles to be coated so that substantially all of the vaporized coating material is deposited on an article to be coated, and is not lost in some undesired portion of the vacuum system.

These and other aspects of the invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing in which,

Fig. l is a schematic vertical section of the presently I preferred embodiment of the invention, and

Fig. 2 is a view taken on line 22 of Fig. 1.

The vacuum coating apparatus comprises an outer vessel 10 which includes a horizontal cylindrical case 12 having an outwardly turned flange 14 at each end.

The rear end of the outer vessel is closed by a circular rear plate 16 secured by bolts 18 to the flange on the rear end of case 12. A conduit 19 attached to the rear plate is adapted to be connected to a vacuum system (not shown) and provides means for evacuating the outer vessel.

The forward end of the case 12 is closed by a circular front plate 20 secured by bolts 22 to the flange at the front end of the case. A hollow rotatable shaft 24 is journaled through the center of the rear plate and is driven by a motor 26.

A processing chamber 28 is coaxially disposed within the outer chamber. The processing chamber is a sixsided polygon in cross-section, and its sides are rectangular plates 30 placed edge to edge along their longer sides. The rear end of the processing chamber is closed by a circular plate 32 secured to the rear edges of the plates 39 by any suitable means such as welding or screws (not shown).

The inner end of the shaft 24 is rigidly attached by any suitable conventional means to the rear surface of the plate 32 so that the processing vessel is rotatable about its longitudinal axis within the outer: vessel.

The front end of the processing chamber ispartially closed by an annula'rfring 34 having a central opening 36. An elongated rectangular boat 38 is attached tothe inside surface of thefront' plate 20 andextendscoaXially into the processing chamber. The boat 38 is adapted to contain the coating material to be evaporated, as well as cathode sputtering devices, or glow discharge plates as may be required for any desired coating operation. These elements may be conventional, and since they are well known, are not illustrated. A heating element 39 is sealed through front plate 20 and disposed in intimate thermal contact with the boat so that the boat and material to be evaporated can be heated by the application of electrical power from a source (not shown) connected to the heating element.

A diaphragm 40, having a central opening of the same shape and slightly larger than the cross-section of the boat 38, is secured to the inner face of the front plates 20 by brackets 42 to reduce the tendency of the coating material to escape from within the processing chamber.

The articles 44 to be coated are attached to the inside surface of the processing chamber walls by brackets 46. An electric heating coil 48 is wound around the outside surface of the processing chamber and is carried out of the vacuum apparatus through a vacuum-tight seal in the opening 50 in the hollow shaft 24. The terminals (not shown) of the heating element are supplied electric current from a conventional source (not shown) by the use of conventional commutators (not shown) which permit the shaft and processing chamber to rotate while current is supplied to the electric heating coil.

The apparatus is operated as follows. The articles to be coated are secured within the processing chamber to the brackets 46, and the end plate 20 is fastened to the front of the case 12. The heating element is turned on and the apparatus is evacuated through conduit 19. The heating element aids the degasing of the apparatus and articles to be coated. After the proper vacuum is reached, the heating element is turned off, and heat is supplied to the boat 38 to evaporate the coating material. The motor 26' is turned on to rotate the processing chamber so that all articles within the processing chamber receive a uniform coating. After the articles are coated to the required density, the heat is cut off. The boat 33 and the apparatus is allowed to cool to a temperature safe for admitting atmospheric pressure without endangering the equipment and the coated articles within the apparatus.

The substantially enclosed processing chamber virtually eliminates the escape of any coating material to parts of the coating apparatus where the coating material would be wasted or cause harm.

This apparatus is particularly important for selenium coating because prior to this invention large and awkward screening devices had to be used to prevent the selenium from diffusing excessively. The elimination of these large and awkward screens permits selenium coating apparatus in accordance with this invention to be much simpler in its construction. A further advantage of the arrangement is the close contact between the article to be coated and the walls of the processing chamber since this makes possible a rapid and uniform heat transfer between the articles and the walls of the processing chamber.

It will. be apparent that the usual devices necessary for control and observation can be installed wherever required and in accordance with technique which is well known to those skilled in the art of vacuum coating.

I'claim: v p

1. Apparatus for coating articles with a vaporizable coating material in a vacuum which apparatus comprises a vacuum-tight outer vessel, means including conduit means connected to the vessel for evacuating the vessel, a substantially enclosed rotatable processing chamber disposed within the outer vessel, a source holder for the coating material disposed within the rotatable chamber, means for supporting the articles to be coated in the interior of the chamber, and means for vaporizing the coating material, the chamber being in fluid communicaass-5,99?

tion with the interior of the vessel only at a portion of the vessel remote from the conduit means to prevent the vaporized coating material from entering the conduit means and contaminating the means for evacuating the vessel.

2. Apparatus for coating articles with a vaporizable coating material in a vacuum which apparatus comprises a vacuum-tight outer vessel, a pair of spaced parallel end plates disposed within the vessel, means connected between the outer peripheries of the end plates to form a processing chamber, the end plates and the means connected between the end plates being rotatably mounted within the vessel, one of the end plates having at least one aperture therein to provide fluid communication between the interiors of the vessel and the chamber, the

other end plate and the means connected between the end plates being impermeable so that only said one end plate is in fluid communication with the interior of the vessel, a source holder for the coating material disposed within the chamber, means for supporting the articles to be coated in the interior of the chamber, means for vaporizing the coating material and a source of vacuumconnected to the vessel in an area adjacent said other end plate to prevent the vaporized coating material from entering the vacuum source.

3. An apparatus for coating articles with a vaporizable coating material in a vacuum as defined in claim 2 including an elongated boat for supporting the coating material,

the boat being attached at one end to one of the end walls of the outer vessel and extending into the processing chamber, and a heating element secured to the outside surface of the means connected between the end plates for varying the temperature within the processing chamber. References Cited in the file of this patent UNITED STATES PATENTS 1,551,850 Schmidmer et al Sept. 1, 1925 2,241,228 Weinhart May 6, 1941 2,322,613- Alexander June 22, 1943, 2,339,613 Becker et all Jan. 18, 1944 2,354,521 Hewlett July 25, 1944 2,469,929 Osterberg. et al. May 10, 1949' 2,540,623 Law Feb. 6, 1951 2,610,606 Weber et al. Sept. 16, 1952 2,768,098 Hoppe Oct. 23, 1956 

